Line a baking sheet with parchment paper.
In a medium/large bowl, combine your flour, baking soda and salt. Gently stir to mix together.
In a mixing bowl/mixer, add the ROOM TEMPERATURE butter, brown sugar and white sugar. Turn it on medium speed for about 3-4 minutes. Do NOT melt butter in microwave - This will drastically change the texture.
Scrape the sides of the bowl and add in the vanilla and the eggs.
Turn the mixer back on medium until the eggs and vanilla are mixed in and scrape the sides again.
Turn off the mixer and add in a small amount of the flour mix. Turn the mixer on low and gradually increase to about medium speed. Slooowly mix in the rest of the flour mixture while the mixer is on.
Once the flour is mixed in, add the chocolate chips slowly.
Turn off your mixer and place the mixer bowl into the fridge. I recommend leaving it in the fridge for at least 30 minutes.
Preheat the oven to 375 degrees.
Scoop out small balls of cookie dough onto the baking sheet after the dough is cold. The dough should be really easy to form into balls after being in the fridge. I recommend 6 medium cookies per large baking sheet or 12 small cookies.
Pop the cookies in the oven for about 8 minutes to check and make sure they are not overcooked. Add 2 minutes at a time until they are slightly brown on the edges. These cookies do set well once they are taken out of the oven. My oven took about 10 minutes but every oven is different.
Once you take them out of the oven, let them sit about 2 minutes before placing on a cooling rack. As soon as they are transferred, place a Reese's mini in the center. When you place them, do NOT push them down. Very gently place them on top.
Add two decorative candy eyeballs to each peanut butter cup before the cookies fully cool.
While the cookies cool, rinse out the medium bowl that you used for flour and set it on top of a small pot of water on the stove on medium high heat.
Add 1/2 of the stick of butter to the bowl and add the other 1/2 bag of chocolate chips. Stir pretty continuously and add more butter as needed until all chocolate has melted and is a creamy texture.
Once it is a creamy texture, remove from the heat and transfer the chocolate to a piping bag or a gallon ziplock.
Cut a very small piece off of the tip of the bag and create 8 spider legs on each cookie by piping out the chocolate. You may want to wait a couple minutes for the chocolate to cool before starting this process. The bag can be hot!
Let the cookies sit for at least an hour so the chocolate can dry. Do not stack cookies.